Tariff pulses having a frequency outside the telephone band of 300 Hz to 3400 Hz, preferably 16kHz, are generated at a central point and are injected in the subscriber termination circuits on the subscriber termination lines for tariff subscriber counting in digital time multiplex telephone switching systems. Such injection takes place at a tariff clock rated dependent on the respective time zone of the circuit to be evaluated. Corresponding counting and display of the tariff pulses then takes place in the subscriber station.
Prior art utilized elaborate circuitry, individual to a line, including two tuned filter circuits and two coupling transformers for injecting tariff pulses. Injection of tariff pulses into individual subscriber termination lines took place independently.